Okay, let's tackle this MCQ about psoriasis. The question is asking which of the options is not seen in psoriasis. First, I need to recall the key features of psoriasis. Psoriasis is a chronic autoimmune condition characterized by hyperproliferation of keratinocytes leading to silvery-white plaques. Common features include well-demarcated erythematous plaques, often on the elbows, knees, scalp, and trunk. The typical morphology is the "silvery scale" and the "psoriatic plaque."

Now, the options aren't provided, but since the correct answer is supposed to be the exception, I need to think about what's not associated with psoriasis. Let's consider possible distractors. Common features of psoriasis include Koebner phenomenon (appearance of lesions at sites of trauma), nail changes like pitting or onycholysis, arthritis (psoriatic arthritis), and a characteristic histopathology showing parakeratosis and acanthosis with a "monotyptical" pattern of epidermal hyperplasia.

If the options are things like "Koebner phenomenon," "nail pitting," "arthritis," and "absence of silvery scales," then the exception would be the one that's not a feature. Wait, no—silvery scales are a hallmark. So if an option states "absence of silvery scales," that would be the exception. Alternatively, if an option mentions a feature like "target lesions" (which are characteristic of erythema multiforme) or "bulla" (seen in pemphigus), those would be exceptions here.

Another possible exception could be "positive Nikolsky sign," which is more associated with conditions like pemphigus vulgaris or toxic epidermal necrolysis, not psoriasis. Psoriasis typically has a negative Nikolsky sign. So if one of the options is a positive Nikolsky sign, that would be incorrect for psoriasis.

So, the core concept here is distinguishing psoriasis from other dermatological conditions based on clinical and histopathological features. The correct answer would be the option that contradicts the known features of psoriasis. The incorrect options would be features that are actually present in psoriasis. The clinical pearl would be to remember that psoriasis has a negative Nikolsky sign, unlike pemphigus, which has a positive one. Also, the presence of silvery scales and specific nail changes are key identifiers. The exception here would be the option that doesn't align with these features.

**Core Concept** Psoriasis is a chronic inflammatory autoimmune skin disorder characterized by epidermal hyperproliferation, silvery-white scales, and distinct histopathological features like parakeratosis and Munro microabscesses. Key clinical features include Koebner phenomenon, nail pitting, and psoriatic arthritis. Distinguishing psoriasis from other dermatoses (e.g., pemphigus) relies on clinical and histological differences.

**Why the Correct Answer is Right** A **positive Nikolsky sign** is not seen in psoriasis. This sign involves the spread of blistering upon gentle pressure and is characteristic of pemphigus vulgaris, toxic epidermal necrolysis, and other blistering disorders. Psoriasis has a **negative Nikolsky sign**, aligning with its

✓ Correct Answer: C. It is premalignant disease